Open Caesar, choose Encode, and enter HELLO, WORLD! with shift 3. Leave “Keep spaces and punctuation” selected. We will follow the ten letters through the alphabet and then decode the result.
1. Inspect the input
The message has ten letters and three other characters: a comma, a space, and an exclamation mark. Only the letters shift. Since the text is already uppercase A–Z, no accent or ligature conversion is needed.
The complete conversion
HELLO, WORLD!Encode; shift 3; A = 0; preserve nonlettersKHOOR, ZRUOG!2. Follow every letter
| Letter position | Input | Index P | (P + 3) mod 26 | Output |
|---|---|---|---|---|
| 1 | H | 7 | 10 | K |
| 2 | E | 4 | 7 | H |
| 3 | L | 11 | 14 | O |
| 4 | L | 11 | 14 | O |
| 5 | O | 14 | 17 | R |
| 6 | W | 22 | 25 | Z |
| 7 | O | 14 | 17 | R |
| 8 | R | 17 | 20 | U |
| 9 | L | 11 | 14 | O |
| 10 | D | 3 | 6 | G |
Select the first H to follow 7 → 10 → K in the step view. Each L becomes O. Unlike a repeating-key cipher, Caesar uses the same shift for every letter.
3. Keep the punctuation in place
The first word becomes KHOOR, followed by the original comma and space. WORLD becomes ZRUOG, followed by the exclamation mark. Together they make KHOOR, ZRUOG!. Punctuation stays in place and does not appear as a letter step.
4. Check decoding
Choose Decode and keep shift 3. K = 10 moves back to 7, or H. G = 6 moves back to 3, or D. Repeating that subtraction for all ten letters returns HELLO, WORLD!.
Your turn
Change only the last word to ZEBRA, keeping the shift at 3. Predict the first letter of that word before converting.